(a) Field of the Invention
The present invention relates to a hydrophone and a pressure balancing device for using for the hydrophone. More particularly, the present invention relates to a hydrophone including a piezoelectric element and a pressure balancing device for using for the hydrophone.
(b) Description of the Related Art
Under water, a water pressure changes according to a depth, and when the depth of water does not change, a water pressure does not change, and this is called a ‘hydrostatic pressure’. However, a sound wave under water changes a pressure by allowing a water particle to generate a vibration of compression waves through a medium of water, and this is called a ‘hydrodynamic pressure’.
A hydrophone is a device that detects sound by detecting a pressure change under water, i.e., a dynamic pressure and converts a voice generating under water to an electrical signal, thereby detecting sound. The hydrophone is designed to detect a wave motion of a frequency from several Hz to several kHz to be widely used as a core part of a sound navigation and ranging (SONAR). Further, the hydrophone may be used in an underwater communication system that uses a high frequency of several tens to several hundreds kHz.
Commercial hydrophones are generally manufactured by mechanically coupling many parts including a piezoelectric element such as piezoelectric ceramic or a piezoelectric polymer such as polyvinylidene fluoride (PVDF), and much time and cost are consumed in manufacturing the commercial hydrophones, and an application range thereof may be limited according to a size thereof.
When manufacturing a sound sensor of a hydrophone using a micro processing technology method such as a micro-electromechanical system (MEMS), a production time and cost of the sensor can be reduced, and nowadays, in order to reduce a manufacturing time and cost, a research of a micro sound/ultrasonic wave sensor that can be used for a hydrophone is widely performed.
However, when a hydrophone is manufactured in a micro size, a problem that a sensitivity is deteriorated in a low frequency range may occur. Particularly, when a piezoelectric element is used, generating charges are not enough due to the piezoelectric element in a low frequency band and thus a sensitivity may be deteriorated due to high electrical impedance and electrical noise of an amplifier. Further, when a sensitive portion of the hydrophone is manufactured in a thin film form, the sensitive portion may be weak to an increasing pressure, i.e., a constant pressure according to the increase of the depth of water.
Accordingly, development of a hydrophone having a structure that can withstand a high pressure while increasing a sensitivity of the hydrophone is requested.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.